Corona generator electrode

ABSTRACT

A corona generator method and apparatus preferably for generating ozone, employing a plurality of corona generating cells each comprising a pair of parallel spaced-apart electrodes having a fired-on coating of porcelain enamel. The electrodes are connected to an AC voltage source of sufficient voltage to generate a corona discharge, and an oxygen-containing gas is passed between the electrodes to generate ozone. A high concentration ozone is produced as well as a large quantity of ozone, without water cooling, and at voltages of approximately 6,000 volts. An equation setting forth, for the first time, the interrelationships between the various parameters in a corona generator is derived by Applicant. According to the invention, the corona power is maximized by maximizing the expression Epsilon /Td, where epsilon is the dielectric constant of the porcelain enamel coating and Td is the dielectric thickness.

mte States :atet 1 1 1 1 3,903,426

Lowther 1 1 Sept. 2, 1975 [54] CORONA GENERATOR ELECTRODE 2,822,3272/1958 Hammesfahr et a] 204/176 3,193,417 7/1965 Kopchak 117/129 X [75]Inventor: Frank Lowthe" Phelps 3,203,815 8/1965 Michael 117/129 x [73]Assignee: Purification Sciences Inc., Geneva, 3,335,080 8/1967 Waller250/541 N Y 3,542,664 11/1970 Guillard et al.. 250/541 3,798,457 3/1974Lowther 250/532 [22] Filed: Sept. 10, 1973 [21] APPL 3 0 PrimaryExaminerF. C. Edmundson Attorney, Agent, or FirmSchovee & Boston RelatedUS. Application Data [60] Division of Ser. No. 141,148, May 7, 1971,

abandoned, which is ii division of $81. No. 379,846, 1 ABSTRACT :Iuly 735 3 A corona generator method and apparatus preferably 2ndalgogmuaggp-m-ifig 0 32 98 31 5 for generating ozone, employing aplurality of corona continuation-in-part of Ser. No. 799,485, Feb. 29,generatmg cells each comPnsmg of parallel 1968, abandoned, which is acontinuation-in-part of spaced'apart eiectrodes havmg a fired'on coatmgof Scr. No. 612,751, Jan. 4, 1967, abandoned porcelain enamel. Theelectrodes are connected to an AC voltage source of sufficient voltageto generate a 52 us. 01. 250/532; 117/129; 204/176 Corona discharge, andan Oxygen-Containing gas is 51 Int. c1. c0113 13/12; 00113 13/10 passedbetween the electrodes to generate ozone- A [58] Field of Search117/129; 204/176, 290 R; high concentration Ozone is Produced as well asa 250 532 541 large quantity of ozone, without water cooling, and atvoltages of approximately 6,000 volts. An equation 5 References Citedsetting forth, for the first time, the interrelationships UNITED STATESPATENTS between the various parameters in a corona generator 0 0 7 898 Ad r 250 532 is derived by Applicant. According to the invention, 3 8 111 i 250238 the corona power is maximized by maximizing the ex- 1 53ll96M1925 250/539 pression e/T,,, where epsilon is the dielectric constantl:8()3:600 5 1931 Daily 250/541 of the Porcelain enamel coating and T11is the dielec- 2,128,455 8 1938 Darling 250/532 Iric thickness-2,309,616 1 1943 Bagby Ct a1. 250/536 2,345,798 4/1944 Daily 250/537 23Clam, 23 Drawmg F'gures PATENTED 35F 2 975 SHEET FIG. 7

INVENTOR FRANK E. LOWTHER FIG. 6

PATENTEUSEP 2197s SHEET 5 OZONE CAPACITY |0,000 lb/doy LOGARITHMIC SCALEOF A v0 5,000

e 5 900,000: 900,000 |,000 lb/doy 005300- |00 lb/doy 10,000- |0 Ib/doyIb/duy I I I I I I .00| .01 0| 1.0 5 l0 IOO LOGARITHMIC SCALE OF TdINVENTOR FIG. E5

FRANK E. LOWTHER PATENTED EP 2 @15 SHEET Mimi IPCBw E0 20 mm om INV ENTOR FRANK E. LOWTHER wm 405.200 mw Om mwkwikkss IONT 92 ATTORNEYPATENTEB SEP 2W5 0 1 m w E INVENTOR FRANK E. LOWTHER 5 W )AWQ w TEmEEOmQ/ZKP mNN mmm mmm @NN NQ 0m. v: N: mmoo mos/Dc 3618 N3 ATTORNEYPATENTEDSEP 2191s SPEET wmT INVENTOR FRANK E. LOWTHER ATTORNEY PATENTEDSEP 2 I 75 SHEET INVENTOR. FRAN K E. LOWTHER ATTORNEY CORONA GENERATORELECTRODE REFERENCE To RELATED APPLICATION This is a divisional of mycopending application Ser. No. 141,148, filed May 7, 1971, and nowabandoned, which was in turn a continuation-in-part of my copendingapplication Ser. No. 709,485, filed Feb. 29,1968, and now abandoned,which was a continuation-in-part of my application Ser. No. 612,751,filed Jan. 4, 1967, and now abandoned. Application Ser. No. 141,148 wasalso a continuation-in-part of my copending US. patent application Ser.No. 830,248, filed June 4, 1969, now U.S. Pat. No. 3,798,457.Application Ser. No. 395,180, filed Sept. 7, 1973 and application Ser.No. 379,846, filed July 16, 1973, are also divisionals of ap plicationSer. No. 141,148.

BACKGROUND OF THE INVENTION 1. Field of the Invention This inventionrelates to corona generators and in particular to commercial large scaleozone generators.

2. Description of the Prior Art Present commercial ozone generators (asdistinguished from very small and inefficient generators capable ofproducing less than 1 pound-of ozone a day) are used primarily incertain chemical processes and other applications requiring ahigh'degree of sterilization, unobtainable by the use of well-knownchemical oxidants or disinfectants. Althoughbenificial in many othermajor applications, such as treatment of industrial waste water orsewage, for example, commercial ozone generators are not usedextensively,'because the ozone is produced in a highly diluted'formbyequipment that is costly, bulky, complicated, and expensive to operate.According to the accepted and usual practice in commercial ozonegenerators, the corona dis charge for producing ozone is generated byapplying a voltage in the order of from 10,000 to 20,000 volts across aglass tube, having walls approximately 100 mils thick, with a conductivecoating on the inside, and a metallic conductor adjacent the tubesoutside surface. In such apparatus, operating at 15,000 volts, forexample, the actual ozone output is in the order of less than 2 ouncesper day square foot of generating area under normal atmosphericconditions. Further, such bulky apparatus requires water cooling andthousands of gallons of water must be pumped through the apparatusdaily. Attempts have been'made to make commercial ozone generatorsemploying, for example, mica, oil paper, plastic, glass, and rubberdielectrics, either as separate sheets or coate'donto an electrode byimmersion or painting, but all such'attempts have failed because, forexample, either'a high voltage application was required to obtain evenminimal amounts of ozone,

or there were limitations'in the configurations-that the generatingdevices would assume, or thedielectric would burn through after alimited number of hours of operation,

It is an object of the present invention to provide a ozonewithout'water cooling and at relatively low voltages. The presentinvention teaches the importance of using a thin, hard procelain enameldielectric coating free of bubbles and free of conductive particles, and

also of minimizing the dielectric thickness and maxi mizing thedielectric constant to produce an unexpected substantial increase inuseful corona power per unit of dielectric area, and thus acorresponding increase in ozone yield. For example, for a givendielectric constant and voltage of 5 mil dielectric produce 8 times asmuch ozone as a 40 mil dielectric, and 20 times as much as the usual 100mil dielectric, operated according to the previous method. Also, for agiven voltage, a five mil dielectric with a dielectric constant of 100,for example, produces 400 times more ozone than a conventional 100 milglass dielectric for a given dielectric surface area. Additionally, by'using a fired on procelain enamel dielectric coating with a hightemperature softening point, a reliable, long lasting assembly isprovided, and at the same time, the ozone output per unit of dielectricgenerating area issubstantially increased fora given voltage. i v

A further object of the present invention is to provide an improvedcorona generator for producing ozone, that is inexpensive,durable,rugged and relatively simple to manufacture.

' SUMMARY 0E THE INVENTION IA'Corona generator including a plurality ofairtight corona generator cells, each cell including a pair of parallel,spaed-apart, electrodeseachhaving a thin, hard, fired-on porcelainenamel coating having a high softening point temperature. The coronapower and thus the ozone yield are maximized by maximizing theexpression (/Td, where epsilon is the dielectric constant and Td is thedielectric thickness, such that (with Td in mils) the expression (/Tdisgreater than 0.10. Oxygen containing gas (for example, air or oxygen)is passed between the electrodes, spaced a predetermined optimumdistance apartfland'the electrodes are. connected to an AC voltagesource having a frequency of between about H2 and 40 KHz and having avoltage of between about, the coron start voltageand 15,000 volts. Thegenerator is cooled by forced :air cooling with-the external surfaces ofthe electrodes in heat exchange relationship with cooling ducts. Thecombined total dielectric thickness (Td) for the two coatings for each"cell is preferably less than about 40 mils and is preferably about 18mils, and the air gap Ta is prefera bly in the range of 5-100 mils. Thelength of the air gap is predetermined in accordance with the thicknessof the' dielectric, the relative dielectric constant, the gas pressure,and the magnitude of the applied voltage. The hermetically sealed cellscan be operated at a pressure higher or lower than ambient, for example,the cells can be operated at any pressure in the range of from at leastabout 0 to 30 psia.

A BRIEF DESCRIPTION OF THE DRAWINGS The present invention will be morefully understood by'-referen'ce to the following detailed descriptionthereof, when read inconjunction with the attached drawings, whereinlike reference numerals refer to like elements and wherein;

FIG. 1' is a fragmentary, plan view of a'corona generator according toone embodiment of this invention;

FIG. 2 is an enlarged, cross-sectional view taken at line 2'2 of FIG. 1and illustrating schematically typical circuitry to create the-corona; II FIG. 3 is a view in perspective, partly cut away, illustrating anothertype of conductor, according to the present invention; 1

FIG. 4 is an enlarged end elevation of a corona generator assembly,according to another embodiment of the present invention;

FIG. 5 is an enlarged side elevation, partly cut away, of the embodimentshown in FIG. 4;

FIG. 6 is a plan view of the embodiment shown in FIGS. 4 and 5;

FIG. 7 is a greatly enlarged cross sectional view of the generatingmembers illustrating certain of the parameters according to the presentinvention;

FIG. 8 is a graphical illustration of the useful corona power in wattsper square inch as a function of voltage and dielectric thicknessaccording to the principles of the present invention;

FIG. 9 is a graphical illustration of the optimum air gap as a functionof voltage and dielectric thickness according to the principles of thepresent invention;

FIG. 10 is a graphical illustration of the useful corona power in wattsper square inch as a function of dielectric thickness and air gapaccording to the principles of the present invention;

FIG. 11 is a graphical illustration of the advantages of the presentinvention, showing the approximate amount of ozone per day that can begenerated with dielectrics of various thicknesses;

FIG. 12 is a front elevation of the corona reactor 10 showing thecontrol panel 20 thereof;

FIG. 13 is a partly broken-away side view of the corona reactor 10 ofFIG. 12;

FIG. 14 is a partly broken-away plan view of the corona reactor 10 ofFIG. 12;

FIG. 15 is a schematic flow diagram for the fluid reactant flow;

FIG. 16 is a simplified, schematic flow diagram show ing the reactantflow into, through, and the reaction product flow out of, the coronareactor core 14 of the present invention;

FIG. 17 is an electrical schematic circuit diagram of the power supplyof the present invention;

FIG. 18 is a front, plan view partly broken-away, of one embodiment of acoron reactor cell of the present invention; 7

FIG. 19 is an enlarged, partial, horizontal, crosssectional view throughthe corona reactor cell of FIG. 18 taken along the line I9-19 of FIG.18;

FIG. 20 is a vertical, partial, crosssectional view through the coronareactor cell of FIG. 18, taken along the line 20-20 of FIG. 18;

FIG. 21 is an electrical schematic circuit diagram showing theindividual corona reactor cells of a corona reactor core connected inseries according to the present invention;

FIG. 22 is an electrical schematic circuit diagram showing the coronareactor cells connected in combination series-parallel; and

FIG. 23 is an electrical schematic circuit diagram showing theindividual corona reactor cells connected in parallel.

DETAILED DESCRIPTION OF THE PREFERREDv EMBODIMENTS Referring in detailto FIGS. 1 and 2, reference numeral 10 refers generally to a coronagenerator assembly that includes a flat piece of metal 1 1, which may beany type, such as iron, steel, copper, or an alloy, for example.Decarbonized steel, or stainless steel, however, is preferable becausethere is less tendency for carbon particles to spall during firing andbecome embedded in the coating. The metallic piece 1 1 is coated withone or more than, hard layers of porcelain enamel 12. In applying thecoating, the metallic piece is first pickled in any well-known manner,or in the case of stainless steel sandblasted. The etched metal piece 11is than sprayed with precelain enamel, and fired at approximatelyfifteen hundred degrees Fahrenheit to harden and bond or fuse theprecelain 12 to the surface of the metal 11.

Porcelain enamel is preferable in that it is inexpensive to apply in athin uniform layer; and it has a relative dielectric constant in theneighborhood of from 5 to 10. Other dielectric materials having asoftening point equal to glass or above, could be employed, if theycould be fabricated or coated in a uniform layer that is thin enough toobtain the benefits of the teachings of this invention, which will bediscussed hereafter.

Deposited, by any well-known method, on the surface of the porcelainenamel 12 is a metallic grid 14 adjacent which the corona or silentelectrical discharge occurs. This metallic grid may be a conductivepaint, for example, that is applied to the porcelain surface.

A transformer 15 has a secondary winding 16 which is connected by itswire 17 to the metallic grid 14 at connector 18, which may be a solderedjoint, for example. The winding 16 is also connected by its wire 19 tothe piece of metal 11 by any conventional connenctor illustrated at 20.A two point switch 21 may be used to selectively connect resist 22 inthe circuit of the secondary winding 16 to reduce the power of theelectrical discharge, and thus the rate of ozone generation, for odorcontrol application in limited areas. A primary winding 23 of thetransformer 15 is adapted to be connected to ordinary 1 10 volt ACcurrent by plug 26.

Referring to FIG. 3, reference numeral 30 refers generally to a coronagenerator for producing ozone, employing a cylindrical electrodestructure 31. The generator 30 has a base 32, which may be of anysuitable material such as wood or plastic. The base 32 has a circulargroove 33 to receive one end of the structure 31 for holding it inposition relative to the base 32. The structure 31 has a fired-onporcelain enamel coating 34 on a rtietallic cylinder 34, as discussed inconnection with the coating 12 of FIG. 1. In intimate contact with thecoating 34 is a metallic screen 35 that is fastened securely by metallicbonds 36 and 37. A transformer 38 is positioned inside the structure 31and fastened to the base 32 by screws 39. The secondary winding oftransformer 38 is shown connected to cylinder 34' and screen 35 by wires40. The primary winding is adapted to be connected to a conventionalvoltage source by plug 41 connected to wire 42. Wires 40 and 42 mayextend externally of the cylinder through slots 43 and 44 in the base32. A perforated cover (not shown) may be placed over thedielectric-conductor structure 31 for protection.

Referring to FIGS. 4 and 6, reference numeral 45 designates generally acorona generating assembly according to another embodiment. The assembly45 comprises rectangular sheet metal conductive members 46 and 47, bothsides of which have a thin, hard coating of fired-on porcelain enamel 48as described in connection with the previous embodiment. Mountedparallel and spaced from the plates 46 and 47 are flat, metal conductivemembers 49, 50, and 51. As used in the present specification and claims,the term parallel as applied to the electrodes is not limited to flatelectrodes, but also includes cylindrical, uniformly spacedapartelectrodes as shown in FIG. 3. The flat plates 49, 50, and 51 arerectangular and have an area of smaller dimensions than the coatedplates 46 and 47, to prevent arcing between front and rear edges 52 ofplates 49, 50, and 51, and corresponding front and rear adjacent edges53 of coated members 46 and 47. The plates 49, 50, and 51 are positionedso that their smaller dimension is parallel to the air flow to present alarger frontal area. Retaining members 54 and 55, which may be of asuitable insulating material, such as polyvinylchloride, for example,hold the coated members 45 and 47, and the conductors 49, 50, and 51 inparallel spaced relation to each other a predetermined distance. One endof coated members 46 and 47 fits in slots 56 of plastic member 55. Oneend of the plates 49, 50, and 51 fits in slots 58 of the plasticretaining member 54, and the other end of the plates 49, 50, 51 and fitsin slots 50 of the plastic retaining member 55. Plastics end plates 60and 61 hold the members 54 and 55 together by steel pins 62 and 63 whichextend through bores 64 and 65 of the members 54 and 55. The steel pin63 fits in holes in plates 49, 50, and 51 that align with the slots 59when mounted in the member 55.

The holes in the plates 49, 50, and 51 are slightly smaller than the pin63 so that when the pin 63 is inserted, it tightly engages the plates49, 50, and 51 to connect them together electrically. The pin 63 may bethreaded at the ends to receive nuts 66 to complete the assembly. Asteel pin 67 extends through holes 68 adjacent the corners of the coatedplates 46 and 47. The pin 67 is of such diameter that it snugly engagesthe metal portion of the coated plates adjacent the periphery of theholes 68 to connect them together electrically.

One terminal of a transformer 70 is connected by a wire 71 to pin 67.The other terminal of the transformer 70 is connected by wire 72 to nut66. Upon application of the voltage from the transformer 70 a corona isgenerated between one surface of the coated plate 46 and the opposingsurface of conductive member 49, and between the other side of thecoated plate 46 and the opposing surface of the conductive member 50.Similarly, a corona is also generated on both sides of the coated plate47 between opposing surfaces of the conductors 50 and 51.

Referring to FIG. 7, the coated plate 47 illustrates a fired-onporcelain dielectric coating having a thickness referred to as Tdv Theconductive or metal plate 51 has a surface 73 spaced a distance Ta fromthe porcelain surface 74. The importance of these parameters will bediscussed hereinafter. Also, in connection with the de scription, it isassumed that the applied voltage is sixty cycle AC voltage.

To understand the principles of the present invention, it must first benoted that according to authoritative sources, the basic thermo-chemicalequation with respect to the formation of ozone is as follows:

30 and 68,200 calories 220 By converting calories to watt hours ofelectrical energy, the theoretical yield of ozone that can be reached at100 per cent efficiency is 0.376 kilowatt hours for each pound of ozonegenerated. The amount of useful corona power for generating a corona interms of the minimum voltage at which a corona can be generated isrepresented by the following formula:

P: 4 F ar a r's) where P corona power in watts F frequency in cycles persecond V, sparking voltage for a given air gap and air pressure 0applied peak voltage V corona start voltage C dielectric capacitance inFarads According to the teachings of the present invention, thedielectric capacitance is converted to terms of thickness of thedielectric, dielectric constant, and the corona generating areaaccording to the following formula or equation:

where e relative dielectric constant T,, dielectric thickness in mils Acorona generating area in square inches The corona start voltage V is afunction of the sparking voltage V,- according to the followingequation:

According to the principles of the present invention, by recognizingthat at standard atmospheric conditions, the sparking voltage isexpressed as related to the air gap length as follows:

(volts per mil of air gap length) Therefore, we obtain the followingformula for useful corona power in watts per unit of corona generatingarea in terms of dielectric thickness and dielectric constant and lengthof air gap in mils.

To further understand the principles of the invention, the air gap T forgiving the maximum useful corona power, may be calculated bydifferentiating the equation 1 above, with respect to the air gap andequating to zero as follows:

(2) (7),) optimum where (T,,) optimum the length of air gap in mils forthe maximum useful corona power per unit of dielec tric generating area.

To determine this maximum corona power at the optimum air gap, theequations l and (2) are combined to obtain the following:

In discussing the operation of the present invention, reference will bemade to FIG. 7 and to the graphical illustration of FIGS. 8 through 12inclusive. The symbols in FIG. 7 and the graphical illustrations areidentical to the symbols used in the following equations.

Referring to FIG. 8, the dashed line represents a conventional 100 milthick dielectric now utilized in corona generators for producing ozonein large quantities. Assuming that the length of the air gap is atoptimum according to the teachings of the present invention as will bediscussed hereinafter, it can be seen that at an applied voltage of15,000 volts, the useful corona power per square inch of generating areais approximately 0.09 watts. In contrast, by utilizing a thin dielectriccoating of five mils, for example, in accordance with the principles ofthe present invention, the useful corona power approximates 1.8 wattsper square inch of generating area.

A thin dielectric also has the advantage of permitting a larger optimumair gap, and thus providing a greater space for the passage of airoxygen through the corona while at the same time obtaining maximumcorona power. For example, with reference to FIG 9, the dashed linerepresents a conventional dielectric similar to the one described inconnection with FIG. 8. At 15,000 applied volts, an air gap ofapproximately 65 mils is optimum. While, a thin dielectric coating, suchas mils, for example, the optimum air gap is in excess of 75 mils. Inpractical applications, it has been found that a very slight increase inlength of air gap (such as l per cent) from optimum reduces some of thecorona losses, and increases slightly the ozone output.

FIG. illustrates the importance of the optimum air gap when utilizing athin dielectric coating according to the present invention. Aconventional hundred mil thick dielectric has an applied voltage ofapproximately 15,000 volts for example, has a broad optimum air gap andtherefore is not as critical for maximum useful corona power. However,for a thin 5 mil dielectric at the same applied voltage, an air gap thatis as little as to mils in error will reduce the useful corona power asmuch as onethird or more.

Also, the lower the applied voltage the less is the optimum air gap; sothat at an applied voltage of 3,500 peak, it is advantageous to use ascreen such as shown in FIG. 3 adjacent to and in intimate contact withthe coated dielectric because the slight curvature of the screen permitsa percentage of its surface to always be at optimum air gap. For smallamounts of ozone, the deposited or painted-on conductor may be used asshown in FIG. 2.

A thin dielectric coating of 5 mils having a relative dielectricconstant of five requires a minimum of approximately 100 volts toproduce a corona. For a dielectric of similar thickness with asubstantially greater dielectric constant, such as 100, for example, acorona 0 ll LIIIl .135 X H A p m n) start voltage in the order ofapproximately 20 volts 8 peak is required. Thus, the higher the relativedielectric constant of the dielectric material, the greater the ozoneoutput per unit of dielectric area for a given voltage and dielectricthickness.

In all electrical devices there are certain losses in the form of heatand light, etc.; and in ozone generators, more or less efficiency,depending on atmospheric pressure and temperature. Therefore, in thegraphical illustration of FIG. 1 1, it is assumed that under normalatmospheric conditions, the actual ozone output per day represents a lowlevel of efficiency as it relates to the useful corona power generatedper unit of dielectric area. Thus, according to the method of thepresent invention, assuming such a low level of efficiency, theproduction of 1 pound of ozone per day requires a dielectric generatingarea of 40 square inches when air or oxygen is passed through an optimumair gap, one wall of which is a dielectric 5 mils thick with adielectric constant of 5 and a voltage of 15,000 peak volts is appliedacross the electrodes, In contrast, assuming the same degree ofefficiency, a conventional thick dielectric of mils requires 900 squareinches to produce I pound of ozone per day. In producing hugh quantitiesof ozone such as 1,000 pounds per day, a thin dielectric of 5 milsrequires 40,000 square inches, and a dielectric of 100 mils requires900,000 square inches.

As heretofore described, the thinner the dielectric for a givendielectric constant and voltage, the greater the useful corona power,and thus the greater the ozone output per unit of dielectric area. Theutilization of a thin dielectric and voltage adjustment is advantageousin applications where it is desirable to have a large variation oradjustable'range between the minumum and maximum ozone output per unitof dielectric area, such as in odor control applications, where thedegree of odor varies widely, for example.

Thus, to obtain substantial benefits from the teaching of the presentinvention, the thinnest'dielectric feasible should be used. In thoseapplications utilizing optimum air gap according to the presentteachings, substantial advantages are realized when the dielectric isless than 40 mils. In other applications, it is considered that thegreatest quantitative advantage is obtained, when a dielectric having athinness of less than 20 mils is used. The expression T, (with T,, inmils) is preferably greater than 0.10.

In one practical embodiment of the invention, a tubular decarbonizedsteel conductor having a fired-on porcelain enamel coating in the orderof 5 mils with a screen conductor in intimate contact therewith wasoperated over 4,000 consecutive hours at 3,500 peak volts withoutfailure or tendency to are.

In another practical embodiment utilizing decarbonized flat steel plateshaving a fired-on porcelain enamel coating 6 mils thick on one plate and12 mils thick on the other place spaced therefrom at optimum air gap andan applied voltage of 7,500 peak voltage produced ozone at the rate of 3pounds per day per square foot of dielectric generating area.

A thin, fired-on porcelain enamel coating with a minimum thinness of 4to 5 mils is practical because it is inexpensive to manufacture usingconventional techniques of firing. It is understood that a thin fired-onglass coating or ceramic piece may be used to the same advantage, or anyother thin dielectric, having a softening point temperature as high asglass or above. Be-

cause of the low softening point temperature, plastics puncture afterlimited use.

Although fired-on porcelain enamel has a dielectric constant of from to10, it has the advantage of being inexpensive in thin coatings ashereinabove described. However, according to the teachings of thisinvention, the higher the dielectric constant, the greater the usefulcorona power per unit of area for a given dielectric thickness andapplied voltage.

THE CORONA REACTOR 110 Referring to FIGS. 12-17 for a description of theover-all arrangement of parts of the present invention, FIGS. 12-14 showa corona reactor 110 of the present invention comprising: a housing 112containing a corona reactor core 114, a transformer 116, a blower 118,and having a front control panel 120. The corona reactor core 1 14 ismade up of a plurality of individual, separately removable, air-tightcorona reactor cells 121.

The heart of the corona reactor 110 is in the corona reactor core 114and corona reactor cells 121, described in detail below under theheading The Corona Reactor Core and The Corona Reactor Cellrespectively. For the present, it will be sufficient to state that:

1. electric power is supplied to the corona reactor core 114 from thetransformer 116 by electrical lead lines 122 and 124;

2. a fluid reactant (when used as an ozone generator, it would be air,oxygen, or an oxygen-containing fluid) is supplied to the corona reactorcore 114 from a source through inlet conduit 126;

3. a fluid reaction product is removed from the corona reactor core 114by an outlet conduit 128; and v 4. the corona reactor core 114 isair-cooled by the blower 118.

The Housing 112 The housing 112 comprises the front control panel 120, arear wall 130, a pair of sidewalls 132 and 134, a cover 136, and a floor138 spaced above the surface upon which the corona reactor 1 issupported by legs 140. The cover 136 is made easily removable, by meansof screws (not shown) or other known type of connecting means, toprovide a convenient means of access to the interior of the housing 112,especially for the addition and/or removal of individual corona reactorcells 121 to the core 114. The cover includes an air exhaust opening142, above the corona reactor core 114, covered by a wire screen 144.The floor 138 includes an air inlet opening 146 below the blower 118.

The housing includes a sub-floor 148 spaced by means of legs 150 asufficient distance above the floor 138 to accomodate the blower 118.The sub-floor 148 supports the corona reactor core 1 14 including aclamp device 152 (of a quick connectdisconnect type to be describedbelow) for securing the individual corona reactor cells 121 together ina modular arrangement.

The Control Panel 120 Referring now to FIGS. 12, 15, and 17, a fluid conduit and control system 154 (FIG. includes the inlet and outlet conduits126 and 128 connected to the individual corona reactor cells 121 of thecorona reactor core 114. The flow rate into, through and out of thecorona reactor core 114 (see FIGS. 15 and 16) includ- 10 ing theconduits 126 and 128, is indicated by a fluidflow meter 156 on thecontrol panel 120, and is controlled by a flow control valve 158 (FIG.15) in outlet conduit 128, having a corresponding control knob 160 (FIG.15) connected thereto and positioned on the control panel 120 andlabeled Flow Control. The fluid-flow meter 156 can be of any standardtype, such as those using a vertically movable ball indicating cubicfeet per minute of fluid flow.

The pressure of the fluid in the system 154 is indicated by a pressuregauge 162 on the control panel 120 and can be controlled by a pressureregulator valve 164 (FIG. 15) in inlet conduit 126 and having acorresponding pressure control knob 166 (FIG. 12) connected thereto andpositioned on the control panel 120 and labeled Pressure Regulator.

A convenient feature of the present invention is the provision of asampling fluid outlet conduit 168 (FIG. 15) connected to outlet conduit128. A sampling valve 170 (FIG. 15) is connected in sampling outletconduit 168 and is connected to a corresponding sampling valve controlknob 172 (FIG. 12) on the control panel 120 labeled Sampling Valve.

With reference to FIG. 12, fluid connection can be made to theabove-described three fluid conduits 126, 128 and 166 of the fluidconduit system 154 directly on the front panel 120 as follows. An inletconnector 174 positioned on the lower left-hand portion of control panel.120, is connected to the end ofinlet conduit 126; an outlet connector176 on control panel 120 is connected to the end of outlet conduit 128;and a sampling connector 178 is connected to the end of the samplingconduit 168.

Referring now to FIGS. 12 and 17, the electrical power supply circuit180 of the present invention includes a power source 182 of, forexample, 120 volt and 60 Hz, connected to the corona reactor core 114through the transformer 116. A power ON-OFF switch 184 is connected inthe circuit 180 and is positioned on the control panel 120. A power-onlight 186 is connected in the circuit 180 and is positioned on thecontrol panel 120 adjacent the switch 184. The light 186 is energizedwhen switch 184 is closed and indicates visually when the power is on.As shown in FIG. 17, the closing of switch 184 also energizes the blower118.

The power applied to the corona reactor core 114 is controlled by avariac 188 connected to a power control knob 190 located on the controlpanel 120 and labeled Power Control. The amount of power supplied to thecorona reactor core 114 is indicated by a watt meter 192 located on thecontrol panel 120.

The Corona Reactor Core 114 Referring to FIGS. 13 and 14, the coronareactor core 114 comprises a plurality of individual corona reactorcells 121 held together in the clamp 152. The individual corona reactorcells 121 will be described in detail below with reference to FIGS.1820.

The corona reactor core 114 is electrically connected to transformer 116by means of the pair of electrical lead lines 122 and 124. The variousmodes of electrically connecting the individual corona reactor cells 121will be discussed in detail below under the heading THE ELECTRICALCIRCUITS.

The fluid connections to the corona reactor core 114 are as follows. Theinlet conduit 126 is connected to an inlet manifold 194 (FIGS. 13 and14) on one side of the corona reactor core 1 14. The outlet conduit 128is connected to an outlet manifold 196 (FIG. 14) located on the oppositeside of the corona reactor core 114. As will be described in more detailbelow, each of the corona reactor cells 121 have an inlet tube 198connected to the inlet manifold 194 and an outlet tube 200 connected tothe outlet manifold 196. The tubes 198 and 200 are connected to themanifolds 194 and 196 by means of connectors 202 (FIGS. 13 and 18), ofany known, suitable type. The connectors 202 are preferably of a quickconnect-disconnect type. Since the number of cells 121 in any core 114can vary, the inlet and outlet manifolds 194 and 196 respectively mayhave openings 204 (see FIG. 18) that are not being used; in such case,plugs 197 (FIG. 14) are connected to openings 204 to close them.

Referring to FIGS. 13 and 14, the clamp 152 includes a pair ofstationary, vertical end plates 206 and 208 supported on the sub-floor148 and held a predetermined distance apart by a pair of spacer tubes210 and 212 and a pair of bolts 214 and 216, respectively, passingthrough the spacer tubes 210 and 212 respectively; the bolts are securedby means of nuts 218. A pair of horizontal support bars 220 and 222 areconnected be tween the vertical end plates 206 and 208. The coronareactor core 114 sits directly on top of the horizontal support bars 220and 222 (a spacer gasket 262, of each of the individual cells 121extends into vertical slots 224 (FIG. 13) in each of the horizontalsupport bars 220 and 222 respectively).

The individual corona reactor cells 121 are vertically oriented and arehorizontally stacked or pressed together by means of clamp 152 and areeasily and separately removable from the corona reator 110 by simplyremoving the cover 136 of the housing 112 and releasing the clamp 152.The individual corona reactor cells 121 are supported on the horizontalsupport bars 220 and 222 between the end plate 206 and a horizontallymovable, vertical pressure plate 226. Pressure plate 226 is movabletoward and away from the corona reactor core 114 by means of anexternally screw-threaded shaft 228 (rotatably connected at a joint 230to the pressure plate 226 and connected in screw-threaded relationshipto end plate 208). A plate 232 connected, by a pair of supports 233 and235, to end plate 208, is provided with a central, internallyscrewthreaded opening 234 in which the shaft 228 is matingly threadedfor rotation. The end plate 208 is provided with an opening 236 toaccomodatea knob 238 rigidly connected to the shaft 228. The knob 238 isrotated to apply or release pressure on the corona reactor core 114through the pressure plate 226. The knob 238 is manually accessible whenthe cover 136 is off.

THE INDIVIDUAL CORONA REACTOR CELLS FIGS. 18-20 illustrate a coronareactor cell 121 comprising a pair of parallel, uniformly spaced-apartelectrodes 252 and 254, each having a bare exterior surface 253 and 255,respectively, exposed to ambient. The electrodes have a dielectriccoating 256 and 258, respectively, on the interior surfaces 257 and 259respectively, of the plates 252 and 254. The spaced-apart electrodes 252and 254 define a corona reaction chamber 260 therebetween. Theelectrodes 252 and 254 are preferably decarbonized steel and thedielectric coating is a high softening temperature dielectric,preferably a thin layer of porcelain dielectric that is free of voids.

Reference is hereby made to other sections of the present specificationfor a description of the method and formulas to be used to determine thepreferred type and thickness of the dielectric coatings 256 and 258, thewidth (inter-electrode or gap spacing) of the corona reaction chamber260, and the applied voltage in the present invention/ The electrodes252 and 254 are preferably rectangular and have a turned or flared edge261 and 263, respectively (see FIGS. 18 and 19) around the entireperiphery of the electrodes 252 and 254. The turned edges 261 and 263are curved away from each other (i.e. away from the adjacent edge of theother of the two electrodes), which permits operation of the coronareactor cell 121 at high voltage without edge sparking. This structureresults in the periphery of each of the composite corona reactor cells121 having a groove 264 (FIG. 19) around the entire periphery thereof,which groove 264 provides for the achievement of a good seal or weld 272around a spacer gasket 262 (to be described in more detail below).

The two electrodes 252 and 254 are maintained a predetermined distanceapart by means of an insulating spacer gasket 262 having a centralopening 266 (see FIG. 18), and positioned between the electrodes 252 and254 around the entire peripheral edge of the cell 121. The spacer gasket262 is preferably made of plate glass with a 10 mil thick siliconerubber gasket on both sides of the spacer gasket 262. The spacer gasket262 can be made of solid silicone rubber or any other suitable material(not metal).

The corona reaction chamber 260 is maintained airtight by sealing theelectrodes 252 and 254 air-tight to the spacer gasket 262 by means of,for example, a weld or bead 272 of silicone sealant (such as that knownas RTV) as shown in FIG. 19. The weld or bead is formed on both sides ofthe spacer gasket 262 around the entire periphery of the cell 121. Thespacer gasket 262 thus performs the functions of defining thepredetermined spacing between the electrodes 252 and 254 and renderingthe cell 121 air-tight.

The fluid reactant is introduced into and removed from the coronareaction chamber 260 of the cell 121 as follows. As stated above, eachcell 121 is provided with an inlet conduit 198 and an outlet conduit200. The inlet conduit 198 is connected to an inlet port 272 inelectrode 252 by means of a connector 275. The outlet conduit 200 isconnected to an outlet port (not shown) in the other electrode 254 bymeans of a connector 277. Since the connectors 275 and 277 areidentical, a description of one is sufficient. The connector 275 iswelded or otherwise connected to the exterior surface 255 of electrode252 at the port 273, which port 273 can include peripheral wall 279extending in a direction away from the chamber 260. The connector275'includes a metallic body 281 having a first cylindrical passageway283 extending partway therethrough and accomodating or receiving theperipheral wall 279 (see FIG. 20). The body 281 of the connector 275includes a second cylindrical passageway 285 perpendicular to the firstpassageway 283 and in fluid communication with the first passageway 283.A tube 287, preferably of metal is welded or otherwise connected to thebody 281 at passageway 285 and extends beyond the body 281 to provide aconvenient means of attaching the inlet conduit 198 to the connector275. The conduit 198 can be slipped over the tube 287 and secured bymeans of a length of wire 289 twisted onto the conduit 198. The outletconduit 200 is preferably constructed in the same manner. Both ports 273(and not shown) can be in the same electrode if desired.

From the above description, it will be seen that each individual coronareactor cell 121 is its own individual pressure vessel, sealed by thespacer gasket 262 and the silicone seal or weld 272 puttied" around theentire periphery of the cell 121 on both sides of the spacer gasket 262.Silicone rubber spacer gaskets and silicone sealant are preferably usedbecause a corona or ozone will not degrade the silicone rubber andsealant, and the silicone rubber and sealant will not degrade the ozone.

In addition to the above described basic structure of the individualcorona reactor cells 121, such cells 121 preferably include certainadditional structure as follows. FIGS. 1820 show a pair of aluminum heatsink spacers 278 and 280 in contact with the exterior surfaces 255 and257, respectively, of the electrodes 252 and 254. The heat sink spacer278 (a description of one is sufficient because they are identical) isformed with a corrugated design having a plurality of oppositelyopening, parallel channels including closed channels 286 and openchannels 288. The heat sink spacers 278 and 280 have several functions:One function of the heat sink spacers 278 and 280 is to act as a heatsink, to remove the heat generated by the corona reactor cell 121 duringthe corona reaction period. To aid in this function, it is preferred toblow cool air through the corona reactor core 114 in a directionparallel to the channels 286 and 288. This is accomplished by means ofblower 118 (see FIG. 13). Thus, as shown in FIG. 14 the corona reactorcells 121 are arranged such that the channels 286 and 288 are orientedvertically so that air entering the corona reactor 110 from the bottomcan be blown vertically up through the corona reactor core 114 and outthe opening 142 in the housing 112. Another function of the spacers 278and 280 is to main tain the adjacent corona reactor cells 121 in spacedapart relationship, when a plurality of such cells 121 are combined toform a corona reactor core 114, and to carry and uniformly distributethe forces resulting from the pressure of the fluid reactant in thereaction chamber 260. The heat sink spacers 278 and 280 also carry anduniformly distribute the forces of the pres sure plate 226 throughoutthe corona reactor core 1 14.

Being electrically as well as thermally conductive, the spacers 278 and280 also provide the additional function of providing an electricalconnection between adjacent electrodes of adjacent corona reactor cells121. The spacers 278 and 280 thus provide convenient elec tricalterminals to which the electrical power can be applied and forelectrically connecting the cells 121 together.

In order to form a corona reactor core 114 containing a plurality ofcorona reactor cells 121, the cells 121 are placed or stacked oneagainst the other as shown in FIGS. 13 and 14, and the electrical andfluid connections made. Regarding FIG. 13 showing the horizontal supportbars 220 and 222 having slots 224 therein, the reason for such slots 224is now clearly seen, -i.e., to provide access room for the spacergaskets 262. V

The conduit 198 carrying the fluid reactant into the reaction chamber260 extends partway through one of the closed channels 286 of the spacer278 and extends through the space 291 between one edge 293 (FIG. 20) ofthe spacer 278 and the adjacent edge 295 of the electrode 252. Theoutlet conduit 200 extends through one of the channels 286 in a similarmanner to that just described for the inlet conduit 198.

FIGS. 18-20 show an additional feature of the present inventioncomprising a silicone baffle 304 to aid in the reaction by preventingthe creation of any dead spaces in the reaction chamber 260. The baffle304 is not a complete, imperforate wall extending across the entirewidth (interelectrode gap) of the reaction chamber 260, but rather asshown in FIG. 19, merely extends partway across the width of thereaction chamber 260.

Further, to prevent arcing the voltage can be decreased. The same (oreven greater) corona intensity can be maintained with a smaller voltageby increasing the frequency, as will be understood by reference to thefollowing equation:

P K V f where:

K is a function of dielectric thickness, dielectric constant, and widthof air gap, in accordance with the teachings set forth in other sectionsof this specification.

P" is the power in watts of the corona discharge;

V is the voltage (in volts) applied across the electrodes 252 and 254;and

is the frequency in Hz.

Typically, the frequency according to this aspect of the presentinvention is in the range of about Hz to 6,000 Hz and the voltage is inthe range of about 2,000 to 15,000 volts peak.

THE ELECTRICAL CIRCUITS Reference will now be made to FIGS. 2123 for adescription of three different voltage driving arrangements of thepresent invention.

FIG. 21 shows the series connected voltage driving scheme of the presentinvention which alleviates the above-described disadvantage in the priorart parallel scheme. As shown in FIG. 21, the transformer 116 has onelead connected to a left-hand outside heat sink spacer 332 of theleft-hand outside or end cell 334 and the other electrical lead from thetransformer 116 is connected to an outside heat sink spacer 336 of theright-hand outside or end cell 338, at the opposite end of the coronareactor core 114. Adjacent plates, (for example plates 340 and 342 ofdifferent but adjacent corona reactor cells 334 and 346) are allelectrically connected together by virtue of a pair of aluminum heatsink spacers 348 and 350, connected thereto.

In this embodiment, the high voltage applied from the transformer 116across the entire corona reactor core 114 will preferably be of theorder of 30,0()0-60,000 volts depending upon the use to which the coronareactor is put.

It is found that the individual electrodes of the individual cells 121act as voltage dividers with the voltage division being governed by thesame laws as govern the corona discharge. It has actually beendemonstrated that, in a stacked (sandwich) array making up a coronareactor core 114, the corona electrode gap of some (or even one) reactorchambers can be twice the distance of that of the remaining reactorchambers, and yet the corond discharge or intensity will be absolutelyuniform throughout every reaction chamber. One reaction chamber was evenmade wedge-shaped in cross-section with virtually no gap on one edge anda full gap on the opposite edge and a preferably uniform corona wasfound to exist therein, with the series electrical mode of FIG. 21 ofthe present invention.

It is further noted that as the exciting voltage is increased from voltsup to the corona discharge start (voltage) point, all reaction chambersstart at exactly the same voltage. This is not true with theconventional parallel mode electrical circuit, where the reactor chamberwith the smallest gap lights first, the second smallest lights second,etc. The uniformity of corona produced by the present invention greatlyfacilitates the ease and economy of manufacture.

FIG. 22 shows a combination series and parallel electrical connectionwherein a smaller voltage can be employed that is used in the embodimentin FIG. 21 where the voltage is supplied across the entire stack(sandwich) or array of corona reactor cells 121 of the corona reactorcore 114. In FIG. 22, one electrical lead 124 from the transformer 116is connected to the two outside end heat sink spacers 310 and 312 (orthe adjacent electrode thereof) of the two outside corona reactor cells314 and 316, respectively. The other electrical lead 122 from thetransformer 1 16 is applied to the two adjacent electrodes 318 and 320of the two middle corona reactor cells 322 and 324, respectively, byconnecting the lead line 122 from the transformer 116 to the spacers 328and 330 connected to the electrodes 318 and 320 respectively. Theoperation of this embodiment of the present invention hascharacteristics of both the parallel and the series electrical circuitsdiscussed above. The voltage to be applied to a corona reactor unit 114having eight corona reactor cells, as shown in FIG. 22, will beapproximately 20,000 to 50,000 volts peak.

FIG. 23 shows a completely parallel electrical ar rangement in which aplurality of corona reactor cells 121 are connected in parallel. Asstated above, the heat sink spacers 278 and 280 provide electricalconnection between adjacent electrodes of adjacent cells. As shown inFIG. 23, the adjacent electrodes of adjacent cells have the samepolarity and are electrically connected together. Electrical connectionfrom the transformer 116 is made directly to the heat sink spacers 278and 280. This parallel system is the preferred electrical arrangement.

EXAMPLE The preferred parameters for a typical run using the coronareactor 1 of the present invention to generate ozone are as follows:

The reactant was air.

The pressure in the individual corona reaction chamber was about 10 psi.

The power applied was 400 watts.

The flow rate was 1 CFM.

The number of corona reactor cells in the corona reactor core was 8.

The corona electrode gap (electrode spacing) was 60 mils.

The voltage was 12,000 volts peak for each cell.

The frequency was 60 Hz.

The ozone yield was 1 pound per day.

It is to be understood that the above description of the presentinvention has been made with reference to the preferred embodimentsthereof and that the present invention is not limited thereto. Forexample, it is within the scope of certain aspects of this invention touse a plurality of tubes or other geometric shapes in place of theelectrodes shown in the drawings, and such tubes and other shapes canalso be stacked or sandwiched together in a modular array, for easyindividual removal and insertion. Such tubes and other shapes can beconnected in the series mode of the present invention. Further, othermaterials can be used than those specifically set forth above. Althoughthe preferred use of the present invention is in the generation ofozone, it is to be understood that other reactants can be introducedinto the corona reactor core 114 and subjected to a corona reaction toproduce various reaction products as is known in the art.

Further, it is not necessary for each of the electrodes 252 and 254 tohave a dielectric coating; one electrode can have a dielectric coatingand the other electrode can be bare metal but with some sacrifice inozone yield.

THE PREFERRED PORCELAIN ENAMEL As defined by the American Society ForTesting & Materials, porcelain enamel is a substantially vitreous orglassy, inorganic coating bonded to metal by fusion at a temperatureabove 800F.. Porcelain enamel is a form of glass in which the mainingredients are silica, borax and soda, i.e., a boro-silicate glass.Other ingredients are added to modify the properties to obtain thedesired expansion, fluidity, adherence, hardness, etc.

The batch of raw materials is melted in a special furnace called asmelter at a controlled time and temperature. It is then quenched bypouring the molten glass, which is at about 2,200F., throughwater-cooled rollers. The sudden chilling forms flakes of solid glasswhich is called Frit. The resulting properties of the frit are as much aresult of the smelting techniques as they are of the formulation of rawmaterials. Two companies smelting the same formula would not necessarilyobtain identical frits.

The frit is the basic ingredient of a procelain enamel. But to apply theenamel, the frit must be ground fine. Water is used as the vehicle andclay and salts are added to keep the frit particles in suspension andgive it sufficient viscosity or set. The mixture is ground in a ballmill and all the additions other than the frit are referred to as milladditions. These additions within limits also tend to modify theproperties of the enamel.

For use with the high dielectric strength procelain enamel coating ofthe present invention the electrode on which it is coated is preferablyde-carburized steel as the base metal, this is a special steel withextremely low carbon produced specifically for porcelain enamelling. Itis less susceptible to enamelling defects than conventional enamellingsteel. The metal is prepared by conventional enamelling proceduresincluding cleaning in a hot commercial soak cleaner and thorough rinsingand then etching in a 6 percent by weight solution of sulphuric acid atF. for about 8 minutes. Following another rinse the electrode isimmersed in'a solution of nickel sulphate for about 10 minutes. Thestrength of the solution is 1 ounce per gallon and the pH. is controlledto between 3 and 4. After the nickel bath the electrode is neutralizedand dried.

Then the porcelain enamel coating of the present invention is applied byfirst applying a ground coat to at least one of the electrodes and thenapplying a cover coat.

The ground coat is applied by spraying to a fired thickness of 2.5 mils.The ground coat composition is:

90 parts l0,3l frit (Chicago Vitreous) parts 2,927 frit (Penco) 3 partsSyloid 255 (W.R. Grace Co.) (synthetic colloidal silica) 50 parts waterThe approximate composition of the 2,927 frit is:

Silica 40% Boric Oxide 207: Alkali 25% (Sodium and potassium oxide)Alumina 3% Cobalt, manganese and nickel oxide 4?! Calcium fluoride 67:Calcium, magnesium and copper oxides 2% lOOVz The approximatecomposition of the 10,310 frit is:

Silica 6571 Boric oxide 107? Alkalais l 171 (Sodium and Potassium oxide)Alumina 37! Cobalt, manganese and nickel oxide 4'71 Calcium andmagnesium oxide 77:

It is ground in a ball mill to less than 1 percent by weight retained ona 325 mesh screen. It is noted that normal fineness for groundcoats is lto percent re tained on a 200 mesh screen.

This frit combination is very effective in suppressing iron oxidepenetration into the coating while being fluid enough to permit themolten enamel to flow into a smooth dense coating. Conventional groundcoats all contain clay and various soluble salts to suspend theparticles in water and which also produce a considerable amount of gasbubbles in the fired coating. The ground coat of the present inventionis virtually bubble free.

The sprayed parts are dried to eliminate the water and then fired atl,480F. for 3% minutes.

Then a cover coat is sprayed on to the ground coat to obtain anadditional fired thickness of about 4 /2 mils.

The cover coat has the following composition:

100 parts 14890 Frit (Chicago Vitreous) 4 parts Syloid 255 /2 partTitanium dioxide A part Zinc oxide A part Barium chloride /2 partLithium silicate 45 parts Water For 14890 Silica 357! Boric oxide 18%Alkalais l 7'71 Titanium Dioxide 22% Alumina 171 Huorine 571 Phosphorouspentoxidc 29? This is ground in a ball mill to a fineness of one half ofl per cent retained weight on a 325 mesh screen. Conventional enamelsare ground to /2 percent on 200 mesh.

This frit has a high titania content and is very fluid at the firingtemperature. Conventional enamels have clay and various soluble saltsfor suspension of the frit particles in water. We have eliminated allgas producing in gredients and the barium chloride tends to suppress theformation of bubbles in the coating.

The white coat is fired at 1420F. for 3% minutesv Additional coats canbe applied the same way. The resulting coating has a dielectric strengthof 1000 volts or more/mil. of thickness and a dielectric constant ofabout 5.5.

Referring to FIGS. 18-20, for example, the presently preferredconstruction employs the above described ground coat and cover coat onelectrode 152, and employs the ground coat and two separately appliedcover coats on electrode 154, for a total dielectric thickness of about18 mils. The second cover coat is fired at the same temperature and forthe same time as the first cover coat.

While the ground coat does not have as high a dielectric strength asdoes the cover (or white) coat, it is preferred to use a ground coatunderneath the cover coat because it has the property of absorbing metaloxides from the metal substrate and such absorption renders the metaloxides (which are otherwise semiconductive) non-conductive. The covercoat does not have this function, and ifthe cover coats were appliedwithout a ground coat there would be more failures of the coating.

The total thickness on each electrode is preferably less than 20 mils,because above this thickness there is a greater chance of the coatingcracking or flaking off of the metal.

While the above specified composition is preferred, other porcelainenamel dielectric materials can be used as will be understood by oneskilled in the art after reading the present specification. The highestpossible dielectric constant material is employed; porcelain enameldielectric materials have dielectric constants ranging from about 2.5 to10.

According to a preferred embodiment of the present invention, inaddition to eliminating all gas producing ingredients from thecomposition, we also prefer to eliminate all conductive particles fromthe composition to prevent them from possibly causing the dielectriclayer to break down at that point and produce a void in the final thindielectric coating when the voltage is applied across it. One preferredmethod of eliminating such conductive particles is by magneticallyseparating any such particles out using any suitable known namneticseparating system. In addition, conductive contaminant particles arekept from ever getting into the composition during its manufacture anduse by maintaining all surfaces extremely clean and by scrubbing themdown prior to use. The use of several separate layers has the advantagein that although a few imperfections may exist in the porcelain enameldielectric material, that if one does exist in a first layer, it isalmost as surcd that there will not exist another imperfection in asecond adjacent layer at a position exactly overlying the imperfectionin the first layer. And an imperfection in one layer will usually notresult in a breakdown of the entire layer, unless it happens to bein-line" or in

1. A CORONA GENERATOR ELECTRODE COMPRISING A METAL ELECTRODE SUBSTRATEHAVING A THIN, HARD, FIRED-ON COATING OF PORCELAIN ENAMEL HAVING ATHICKNESS OF LESS THAN 20 MILS, SAID COATING BEING FIRED ONTO A SURFACEOF SAID SUBSTRATE AT A TEMPERATURE SUFFICIENTLY HIGH TO BOND SAIDPORCELAIN ENAMEL COATING ONTO SAID SURFACE OF SAID SUBSTRATE.
 2. Thearticle according to claim 1 wherein said electrode is flat and saidcoating has a dielectric constant of at least
 5. 3. The articleaccording to claim 1 wherein said electrode is an etched, decarbonizedsteel electrode and said coating is fired-on at a temperature of about1,500*F.
 4. The corona generator electrode according to claim 1 whereinsaid coating comprises a plurality of separately firEd-on individuallayers of porcelain enamel.
 5. The article according to claim 4 whereinsaid plurality of layers includes a ground coat having a thickness ofabout 2 1/2 mils fired-on at a temperature of about 1480*F., and atleast one cover coat having a thickness of about 4 1/2 mils and fired-onat a temperature of about 1420*F.
 6. The article according to claim 4wherein said coating is fired-on at a temperature of about 1500*F. 7.The article according to claim 6 wherein said coating has a dielectricconstant of at least
 5. 8. The article according to claim 7 wherein saidsubstrate and said coating each have a constant thickness and whereinsaid coating has a flat, smooth surface.
 9. The article according toclaim 8 wherein said substrate is flat over a major portion of its area.10. The article according to claim 9 wherein said surface of saidsubstrate is etched prior to said coating being fired thereon.
 11. Thearticle according to claim 10 wherein said porcelain enamel has a highsoftening point temperature at least equal to that of glass.
 12. Thearticle according to claim 11 wherein the total dielectric thickness Tdin mils of said coating, and the dielectric constant epsilon of saidp.e. are such that the value of the expression epsilon Td is greaterthan 0.1.
 13. The article according to claim 12 wherein said coating isuniform and is free of voids.
 14. The article according to claim 13wherein said coating is free of conductive particles.
 15. The articleaccording to claim 1 wherein said coating has a dielectric constant ofat least
 5. 16. The article according to claim 1 wherein said substrateand said coating each have a constant thickness and wherein said coatinghas a flat, smooth surface.
 17. The article according to claim 1 whereinsaid substrate is flat over a major portion of its area.
 18. The articleaccording to claim 1 wherein said coating is fired-on at a temperatureof about 1500*F.
 19. The article according to claim 1 wherein saidsurface of said substrate is etched prior to said coating being firedthereon.
 20. The article according to claim 1 wherein said coating isuniform and is free of voids.
 21. The article according to claim 1wherein said cotaing is free of conductive particles.
 22. The articleaccording to claim 1 wherein said porcelain enamel has a high softeningpoint temperature at least equal to that of glass.
 23. The articleaccording to claim 1 wherein the total dielectric thickness Td in milsof said coating, and the dielectric constant epsilon of said p.e. aresuch that the value of the expression epsilon /Td is greater than 0.1.